Phase-locked Loop Method Research Articles

DC offset elimination method of Phase-locked loop based on novel generalized integrator

When the renewable energy power is connected to the grid, distortion voltage interference and grid voltage frequency fluctuation will occur, which will cause the inverter output current to be abnormal. So the grid-connected environment of weak grid puts forward higher requirements on the performance of phase-locked loop (PLL). The synchronous reference frame PLL(SRF-PLL) has become a usually adopted method in grid synchronization technique for its simple structure and strong stability. However, the conventional SRF-PLL has insufficient capability to suppress DC offset, which easily causes fundamental frequency and phase oscillations. Therefore, this paper presents a novel generalized integrator(NGI), and according to the presented NGI structure, a modified novel generalized integrator (MNGI) that can eliminate DC offset voltage is proposed. Then a novel PLL based on dual MNGI(DMNGI) is proposed. This method improves the capability of the phase-locked loop to suppress DC offset. At the same time, this paper designs the parameters of the PLL, and the rationality of the novel PLL is tested effectively through the experimental comparison with the other two methods.

Realization of Cascaded H-Bridge Multilevel Inverter Based Grid Integrated Solar Energy System With Band Stop Generalized Integral Control

The high power grid integrated solar energy system (GISES) prefers multilevel inverters for reduced switching losses and lower harmonics in the injected current. The integration of solar PV array with multilevel inverters (MIs) requires a proper selection of multioutput dc–dc converters. Moreover, the performance of two-stage GISES with isolated multioutput dc–dc converters and dc–ac multilevel inverters are less investigated in the literature. In this article, a cascaded H-bridge multilevel inverter with isolated multiple-output zeta converter is used. It exhibits reduced switching stresses and improved efficiency, concerning to multiple dc–dc converters fed MI. The maximum power point tracking method, based on the firefly algorithm, is implemented on the isolated multiple output zeta converter to ensure maximum power extraction at adverse irradiation conditions. The power quality improvement and active power exchange through a band stop generalized integral control, and the grid synchronization is achieved through an enhanced phase-locked loop method. The proposed system is designed and simulated in MATLAB/Simulink, and the results validate the theoretical claims. The performance of the GISES is verified using an experimental prototype developed with the help of a dSPACE Micro Lab Box and a solar PV simulator.

An improved permanent‐magnet synchronous machine sensorless drive based on the fuzzy‐PI phase‐locked loop and the adjustable boundary‐layer FOSMO

This study proposes a variable boundary-layer full-order sliding-mode observer (FOSMO) with a fuzzy proportional plus integral (PI) phase-locked loop (PLL) for the sensorless control of a permanent-magnet synchronous machine (PMSM). The sigmoid switching function-based FOSMO, which includes feedback speed information, is presented and considered as the conventional method. To address the contradiction between the convergence performance and the chatter-reduction ability of the sliding-mode control, a fuzzy logic controller (FLC) is introduced to adjust the boundary-layer thickness according to the estimation error. Furthermore, a real-time parameter tuning module is integrated into the PI regulator of the conventional PLL to adjust its noise bandwidth. Hence, adverse effects of disturbance and external noise, especially under transient operations, can be eliminated. An overall PMSM sensorless field-oriented control scheme incorporating the proposed method is designed, and the corresponding experimental platform is constructed. Several groups of comparative experiments reveal that system chatters are largely reduced using the proposed method under both of the high- and low-speed running conditions and the dynamic anti-interference performance can also be significantly improved under load and speed disturbances. Therefore, the feasibility and effectiveness of the proposed variable boundary-layer FOSMO + fuzzy-PI PLL method are validated.

Resynchronization Analysis and Improvement of Grid-Connected VSCs During Grid Faults

Grid codes stipulate that grid-connected voltage source converter (VSC) interfaced generation units should possess fault ride-through capability during grid faults. Resynchronization with the postfault grid is crucial for this purpose. However, it is not always easy for VSCs connected to a high-impedance weak grid to achieve resynchronization during severe grid faults. This article studies the loss of synchronism (LOS) of VSCs during grid faults. A nonlinear model describing the dynamics of the phase-locked loop (PLL) is developed, and a modified equal area criterion is utilized to identify the crucial factor affecting the resynchronization. The findings show that PLL’s integral regulator is unfavorable for the resynchronization since it probably causes the system operating point to enter negative damping zones and even reverse regulation zones, consequently resulting in LOS. A variable structure PLL method with great simplicity is proposed to improve the resynchronization capability. The method removes PLL’s integral regulator during grid faults to eliminate its unfavorable effect. Experimental and simulation comparisons with existing methods verify the performance of the method.

Synchronization System for Semiconductor Frequency Converters with a Power Supply Network

This article provides a detailed description of synchronization node operation based on the well-known method of a phase-locked loop. It is shown that the phase-locked loop method can be successfully applied in synchronization nodes of valve frequency converters provided that the amplitude of the reverse phase sequence does not exceed 20%. The dependence of the transient time of the measured variable voltage in the synchronization device is obtained depending on the level of asymmetry of the supply voltage, which was estimated by the amplitude of the voltage component of the reverse phase sequence. The dependence of the transition time on the amplitude of the reverse phase sequence is quadratic because of the need to reduce the uniform bandwidth of the second-order filter. The results of the refinement calculation of the metrological characteristics of the synchronization device with account for nonlinear distortions showed that, with the simultaneous presence of nonlinear distortions in the supply voltage curve and asymmetry of the supply voltage, the permissible level of the amplitude of the negative sequence voltage is limited to 10%.

Single-phase flexible arc suppression device based on BSC-SOGI-PLL method for distribution networks

The single line-to-ground (SLG) fault is a research focus, considering it is amongst the top frequent occurrences of faults in distribution systems. The neutral point treatment is crucial for continuous safe operation of distribution systems. However, the traditional arc suppression coil cannot compensate for the active component in ground current. Therefore, we present a single-phase flexible arc suppression device (SFASD) based on backstepping control and second-order generalized integrator phase-locked loop (BSC-SOGI-PLL) method. The SFASD with a cascaded H-bridge (CHB) topology is connected to the neutral point of distribution systems for eliminating the ground current. The comparisons between the BSC-SOGI-PLL and the BSC method concerning the effect of arc suppression are discussed. The effectiveness of the proposed SFASD based on the BSC-SOGI-PLL components for arc suppression is verified on the scale-down experimental platform.

A fast hybrid PLL with an adaptive all-pass filter under abnormal grid conditions

Recently, various phase locked loop (PLL) methods have been improved for a reliable and robust synchronization under non-ideal grid conditions. One of the PLLs is a hybrid PLL (HPLL) which is an improved structure of the quasi-type-1 PLL (QT1-PLL) method. In this paper, an enhanced HPLL that offers both fast transient response and increased disturbance rejection capability for dominant harmonics is proposed. The proposed PLL includes adaptive all-pass-filters (APFs) in pre-filtering stage to eliminate fundamental frequency negative sequence (FFNS) component. Thus, window-width of the moving average filter (MAF) is reduced by three times compared with the HPLL by means of removing the FFNS component. So, the proposed PLL, which is called fast-hybrid PLL (FH-PLL), considerably ensures a fast transient response. Also, in case of grid faults (for example, type-B, type-C, type-D, and etc.), at the same time frequency change occurs, the FH-PLL completely blocks the FFNS component by means of using adaptive DAPF. In this study, it is experimentally implemented HPLL, QT1-PLL, and the proposed FH-PLL methods. The effectiveness of the FH-PLL is verified owing to experimental results and comparison with the QT1-PLL and HPLL.

Single-Phase Phase-Locked Loop Based on Tracking Differentiator

To better capture the phase information of single-phase power grids, a novel single-phase phase-locked loop method is proposed in this paper. The method uses a tracking differentiator as an orthogonal signal generator. Because the generator is sensitive to the input signal’s frequency, the amplitudes of the tracking and differential signals may not be equivalent, causing a failed phase tracking. Therefore, the amplitude correction of the differential signal needs to be done. Then, the corrected differential signal and the tracking signal are both input to the phase detector. To further verify the practical feasibility of the method, the voltage sampling and phase tracking experiments were performed on a digital signal processor-based inverter experimental platform, which is aimed to simulate the grid. The experimental results show that the proposed algorithm has strong dynamic performance and steady-state performance under different states of the power grid, and the phase-locked method has a practical feasibility in single-phase grid-connected applications.

A new SOGI-PLL method based on fuzzy logic for grid connected PV inverter

<p>Phase angle detection of the grid voltage is an imperative part of control in most applications, especially for the synchronization of the current injected by the grid-connected photovoltaic inverters. Consequently, fast and accurate detection of the phase angle, frequency and amplitude of the grid voltage are indispensable data to ensure a correct generation of reference signals and operation of the grid connected inverters. We present in this work a new phase-locked loop (PLL) method for single-phase systems. The novelty is to generate an orthogonal voltage system using a second-order generalized integrator (SOGI), followed by a Park transformation, whose quadrature component is forced to zero by the fuzzy logic, in order to obtain rapid detection and a more accurate picture of the phase angle. Furthermore, simulation results with PSIM software will be submitted to verify the performance and effectiveness of the proposed method strategy. Finally, the experimental test will be used to extract the result and discuss the validity of the proposed algorithm.</p><p> </p>

Harmonic suppression for pulsed load based on improved software phase locked loop method

Harmonic suppression for pulsed load based on improved software phase locked loop method

Photovoltaic inverter control using programmable logic device

Solar power plant system represents the clean energy generation systems which convert and deliver the large amounts of solar radiation energy to the grid. The main purpose of the study is to maximize the amount of energy delivered to the grid from the solar photovoltaic cells. The solar irradiance and the grid voltage are the complex and dynamic system and need the universal solution which can provide more power at high dynamics of changes in external, various conditions. This work focuses on investigations provided in detail for the fuzzy logic-based synchronization technique which significantly increases the energy efficiency of the photovoltaic system. The multi-photovoltaic system’s controller concept was elaborated and evaluated using the programmable logic device, particularly useful for power critical drives. The dynamic responses of photovoltaic system were measured, which refers to the start procedure, solar irradiance, grid frequency and phase angle change. The results of the photovoltaic system investigation are made to appoint the efficiency in relation to the standard solution. The proposed fuzzy logic-based synchronization method delivers more energy to the grid in dynamic states in relation to the standard phase-locked loop method. The normal operation of the photovoltaic system is the dynamic operation. Therefore, the solution described in work allows to increase the efficiency of solar farms.

A Design Method of Phase-Locked Loop for Grid-Connected Converters Considering the Influence of Current Loops in Weak Grid

Phase-locked loop (PLL) with improper bandwidth could lead to potential instability issues for the grid-connected voltage-source converters (VSCs) under weak grid conditions. The current loops of the VSCs can be designed faster as the development of the silicon carbide (SiC) and gallium nitride (GaN) semiconductor materials. It is questionable whether the PLL’s bandwidth could also be designed higher for faster current loop. Hence, the relationship between the bandwidth of the current loop and the bandwidth of the PLL is studied first. It is revealed that the bandwidth of the PLL might not be increased linearly with the increasing of the bandwidth of the current loop, and thus, the traditional design principle, i.e., the bandwidth of the PLL is not higher than one-tenth of that of the current loop, might no longer be suitable. Thus, this paper proposes a design method of the PLL to make the grid-connected VSCs to have adequate stability margin and satisfactory dynamic performances under weak grid conditions. The current loop is designed independently, while the PLL is designed considering the coupling between the current loop and the PLL under weak grid conditions. The simulations and experimental results verify the theoretical analysis and the proposed design method.

Compensation System Design and Comparison of Very High Doppler Frequency Effect

One of the serious problems in the low earth orbit (LEO) satellite communication system is the very high Doppler frequency effect since the LEO satellite system runs very fast to keep the orbit altitude. Especially, this problem produces the critical performance degradation when the broad bandwidth is necessary for the very high speed satellite transmission of the very high resolution image data. As the data speed is increased, the higher efficient communication technology will be required to transmit the high-capacity of data to the ground station. In the LEO satellite communication systems, very large Doppler influence is generated because of the very fast movement of satellite. This Doppler spectrum shift effect, similar to the carrier frequency offset effect, can cause performance degradation in the satellite communication system. Therefore, it is very important to effectively compensate for this Doppler frequency shift. So, in this paper, we analyze this Doppler effect of LEO satellite receiver and propose an efficient compensation system design against the Doppler frequency. Two compensation methods are proposed: pilot method and phase locked loop (PLL) method. As simulation results show, when the SNR is approximately 5 dB or less, the pilot method provides better performance, compared with the PLL method. When the SNR is approximately 6 dB or more, it can be confirmed that the PLL method outperforms than the pilot method, which is almost same to the theoretical performances. Furthermore, it can be said that the PLL method is very spectrum-efficient than the pilot method since it does not require any pilots. However, it is very difficult and expensive to design the accurate, agile, broadband operating PLL system to compensate the very wide range of Doppler frequency shift.

Power Injection on Single Phase Grid System

This paper deals with power injection on single phase grid connected inverter. The simple method is introduced to understand the concept of grid connected systems. A phase Lock Loop (PLL) method estimates the phase-angle of grid system. The output of PLL is used to defines Iref , and the current of inverter becomes a feedback (IL). Both current are derived to produce PWM using current mode controller method. As long as the grid system on fault condition like voltage distortion, therefore the single-phase inverter that connected into the grid should change the role and keep stabilization. The voltages sag and swell are the possible conditions that occurred on a power system. Voltage Sag is an event where the line voltage decreases from the nominal line-voltage for a short period of time. Voltage swell is the event when the line voltage increase from the nominal line voltage. By using PSIM software, the injection and absorption of power into a grid system is verified during a voltage sag, swell, and normal. The simulation shows voltage grid vg, current inverter iinv, current grid, active power P, reactive power Q. The waveform of the measured parameter is analized to define the role of inverter toward grid. the The result shows performance of the proposed inverter to absorb reactive power during swell, and inject reactive power when sagging.

Robust estimation of voltage parameters via a sliding mode observer

Grid voltage parameters are essential for the real-time control and protection in power systems. Current approaches mainly focus on the phase-locked loop methods, but which are slow and sensitive to voltage variations and disturbances. In this paper, the estimation of grid voltage parameters is recast as an observer design problem. A second-order sliding mode observer (SMO) is designed to estimate the grid voltage parameters based on the exosystem model. Moreover, the asymptotic stability of the closed-loop SMO is proved. Simulation and experimental results are presented to illustrate the effectiveness of the proposed approach, which achieves fast response and accurate estimation

A three-phase phase-locked loop algorithm with immunity to distorted signals employing an adaptive filter

This paper introduces a synchronization algorithm for the detection of the fundamental positive-sequence component in three-phase systems. The structure is based on the correlation of the input signal with a complex signal generated from the association of an adaptive filter and a phase-locked loop (PLL) method previously presented in literature. Good disturbance rejection is then achieved, in particular to interharmonics and subharmonics. Simulation and experimental results are presented and discussed in order to demonstrate the performance of the proposed solution when compared with that regarding dual second-order generalized integrator frequency locked loop (DSOGI-FLL), which is often considered to present good disturbance rejection.

Speed Control for Turbine-Generator of ORC Power Generation System and Experimental Implementation

This paper presents a rotation speed estimation and an indirect speed control method for a turbine-generator in a grid-connected 3-phase electrical power conversion system of an organic Rankine cycle (ORC) generation system. In addition to the general configuration mechanism and control techniques that are required in the grid-connected ORC power generation system, the indirect speed control method using the grid-side electric power control and the speed estimation method is proposed for the proper speed control of turbine-generators. The speed estimation method utilizes a digital phase-locked loop (PLL) method that uses a state observer to detect the positive-sequence voltages. A 10 kW system where a Motor-Generator set is used as a turbine simulator and a 23 kW actual system for the grid-connected ORC power generation were designed and manufactured, respectively. This paper includes various experimental results obtained from field tests conducted on actual installed ORC systems.

A New Navigation Message Demodulation Algorithm for Satellite Navigation Receiver

A new navigation message demodulation algorithm for satellite navigation software receiver is researched. The detailed phase and frequency information of the carrier are obtained by analyzing the phase angle of the DFT component of the satellite navigation IF signal, and navigation messages are demodulated by adjusting the initial phase of the adjacent data block is π flipped or not. The detailed implementation steps of the method are presented, and the reason of phase angle discontinuity of kernel function is analyzed and compensated. Finally, the method is verified by simulation and actual signal respectively and compared with the traditional phase-locked loop method. The results show that the carrier frequency accuracy of new algorithm can reach 10 Hz, more precise than traditional method; signal tracking can effectively output navigation message information, the method with data block processing to obtain the phase angle is more suitable for software radio ideas.

Demodulation of Angular Position and Velocity from Resolver Signals via Chebyshev Filter-Based Type III Phase Locked Loop

A high-accuracy demodulation algorithm is required to estimate angular position and angular velocity from resolver signals. In order to improve the estimation accuracy of conventional phase-locked loop (PLL) based demodulation method, a Chebyshev filter-based type III PLL method is proposed in this paper. The proposed method makes PLL become a system of type III tracking loop, which could greatly reduce the theoretical constant deviation in the estimation results of conventional type II PLL in case of variable speed. Meanwhile, the eigenvalues of type III PLL are placed to be the same position as those of a Chebyshev low-pass filter. In this way, demodulation parameters with stronger filter properties can be obtained to effectively suppress the high-frequency measurement noise in resolver signals. Thus, the proposed method can achieve higher demodulation precision compared with the conventional ones. Simulations and experiments are performed to validate the proposed demodulation method.

Research on Power Grid Imbalance and Harmonics Based on Improved Phase-Locked Loop

In the new energy grid connected power generation system, accurately extracting the grid synchronization signals such as frequency, phase and amplitude of the grid voltage is the basis for effective control. A new design method of phase-locked loop (PLL) in static coordinate system is proposed for the demand of synchronous signal detection under unbalanced and harmonic conditions. This method uses the resonator to extract and filter the high frequency harmonics in the grid voltage, and combines the adaptive trap (ANF) and the positive and negative sequence elimination loop (PNSC) to complete the voltage positive and negative sequence separation, and then accurately extracts the synchronous information of the positive sequence voltage of the power grid. The simulation and experimental results show that under the conditions of unbalanced and harmonic grid, the designed PLL can quickly and accurately lock the property of the grid voltage, and has the advantages of high detection precision and strong robustness to frequency fluctuation. It can provide reliable reference signal for the new energy grid connected power generation control.